1. Field of the Invention
The present invention relates to a pump-valve-nozzle unit (PVD) in an elongated arrangement with hydraulic-mechanical boosting.
The structure of modern internal combustion engines, where up to four valves can be provided per cylinder, severely limits the available installation space in the cylinder head for injection systems. Moreover, hydraulic-mechanical boosters are assigned to the pump-valve-nozzle units and must also be accommodated.
2. Description of the Prior Art
German Patent Disclosure DE 39 10 793 A1 relates to a fuel injection apparatus for Diesel engines with at least one pump piston. This pump piston is guided sealingly in a bush and together with the pump body forms a pumping chamber, which during the downward motion of the pump piston communicates by means of a control element with a suction chamber, and via an injection line, the pumping chamber communicates with an injection valve. The object of the invention is to keep the idle volume of the fuel injection apparatus as small as possible, to make high injection pressures feasible. This is attained by providing a permanently open communication in terms of flow between the pumping chamber and the injection valve.
German Patent Disclosure DE 198 99 627 A1 relates to a fuel injection apparatus for internal combustion engines. It includes a high-pressure fuel pump, which communicates on the intake side with a low-pressure fuel supply system and on the high-pressure side with a fuel injection valve that protrudes into the engine combustion chamber. The high-pressure pumping into a high-pressure conduit provided between the high-pressure fuel pump and the fuel injection valve is controllable by means of an electrical control valve, which has an electrically actuatable, displaceable valve member with a valve sealing face. By its valve sealing face, it cooperates with a stationary valve seat to form a sealing cross section. To improve the control times and vulnerability of the control valve to wear, the control valve member and/or a sleeve that guides it are made of ceramic.
In the arrangements of fuel injection apparatuses discussed above from the prior art, pressure pulsations can occur in the system because of the L-shaped arrangement of the valve relative to the injection nozzle.
With the arrangement proposed according to the present invention, an arrangement extending essentially in the vertical direction of a pump part, a valve part adjoining it, and a nozzle part adjoining the valve part, in an injection arrangement can be assured. With this essentially vertically extending arrangement of the pump, valve, and nozzle components, a largely flow-free pressure buildup can be achieved. According to this arrangement, the pump, valve and nozzle components are all located one after the other in hydraulic terms. The elongated arrangement of pump-valve-nozzle units allows a hydraulic-mechanical booster to be flanged laterally to them. Because of the essentially vertically extending arrangement of the pump part, valve part and nozzle part, a length ratio between these parts, that is, between the pump chamber and the control valve chamber and between the control valve chamber and the nozzle chamber, of 1:5 can optimally be achieved. As a result, excessively long injection lines can be avoided; instead, the time constant of an injection is now substantially greater, compared to the time for wave propagation between the individual elements, such as to the nozzle chamber. As a consequence, the pronounced pressure fluctuations that occur in the arrangements of PDE units in the versions of the prior art between the pump components, that is, the pump part, valve part and nozzle part, can be suppressed in the embodiment according to the invention. The adverse effects of such resultant pressure pulsations in lines that are designed as overly long and are at high pressure can cause undesired phenomena such as undesired opening, fluttering or closure of a nozzle needle that opens above that pressure, which in an extreme case can cause unstable needle opening behavior as well as nozzle needles that close again, depending on the rotary speed of the cam that drives the pump body.
With a pump-valve-nozzle unit disposed in accordance with the present invention, these disadvantages can be avoided by means of an inlet bore system which is designed with optimal length ratios. As a result of the elongated arrangement of the pump part, valve part and nozzle part, it is furthermore optimally possible to economize on installation space, so that enough structural space per cylinder of an internal combustion engine is available to provide two high-pressure injection valves, even if these valves are provided with laterally flanged-on piezoelectric actuators for actuating the control valve, together with a hydraulic-mechanical booster received thereon.
Since an additional mechanical boosting is provided on the piezoelectric actuator, the valve chamber can be optimally designed with regard to the length ratios of the line systems. Mounting the hydraulic-mechanical booster by flanging it on laterally results in a simple adjustment of the requisite mechanical stroke courses required to actuate the control valve. Since the actuating unit includes a mechanical booster, in the form of a lever that is pivotable about a pivot axis, the hydraulic boosting volume can be kept small and can be operated at very low pressures (only 6 bar).
Furthermore, the vertical arrangement of PDE units of an injector proposed according to the invention has the advantage that instead of the previously required three to four high-pressure bore intersections in the injector body, now only two high-pressure bore intersections are required in the injector body. To assure a resistance to pressure pulsations of up to about 2000 bar for an injector body for high-pressure Diesel injection systems, the high-pressure bore intersections must be minimized, since they impair the mechanical loadability of the injector body. The high-pressure bore intersections define the limit for the mechanical loading of an injector body, which accordingly sets a limitation to the attainable pressure level in the high-pressure collection chamber (common rail).